Flowering plants pass through three primary post-embryonic developmental stages: juvenile, adult, and reproductive. Recent studies in Arabidopsis have demonstrated that mutations in several key enzymes involved in the biogenesis of smallRNAs accelerate the juvenile-to-adult transition in vegetative growth. These include the microRNA exporter HASTY (HST), the plant-specific protein SGS3, the RNA-dependent RNA polymerase RDR6, the Dicer-like protein DCL4, and the ARGONAUTE protein ZIPPY (ZIP). The current model is that these proteins act sequentially to direct the production of trans-acting siRNAs (ta-siRNAs) that promote the juvenile phase, and, therefore, only indirectly affect phase change. I propose to identify the direct effectors of vegetative phase change using three approaches. First, I will identify and characterize genetic suppressors of zip using a mutant screen. Second, because mutations in the auxin-related genes ARF3 and PIN1 have been shown to partially suppress the zip mutant phenotype, I will explore the role of auxin in vegetative phase change. Finally, I will analyze the function of genes whose expression is upregulated in zip to determine if these genes contribute to the precocious phenotype of this mutation. [unreadable] [unreadable] [unreadable]